The main purpose of this project is to make some contribution to the detailed understanding of benzo(a)pyrene (BP) mutagenic pathway by studying the basis for the stereoselectivity of trans-7,8-diol-9,10-epoxy-benzo(a)pyrene stereoisomers, the possible ultimate carcinogenic metabolites, on the binding to DNA which can then serve as model for other carcinogenic polycyclic aromatic hydrocarbons. This will be accomplished by spectroscopic studies, especially CD, on the binding of pyrene, benzo(a)pyrene, trans-7,8-dihydroxy-7,8-dihydro-BP and trans-7,8-dihydroxy-7,8,9,10-tetrahydro-BP to natural, synthetic DNA's and oligonucleotides. Specific informations to be obtained are: base sequence specificity of each compound, the geometries of the intercalated complexes, the effect of spatial disposition of the hydroxyl group at C(7) and C(8) of the metabolites on the stereogeometry of these complexes, the kinetics and thermodynamic properties on the dissociation and association of these DNA + ligand complexes.